Here's where things get really interesting: incorporating common bass technique. Slapping and popping in this context is rarely seen, but when demonstrated effectively, can produce a very interesting and innovative sound.

Harmonically, we're playing nothing outside a common A blues scale. The right hand technique, as in part 1, will usually be the cause for headache. The S's and P's, as noted in the notation stand for Slap and Pop.

Slap: Using the side-part of the right-hand thumb to literally slap the string to achieve the most percussive, loudest and intense dynamic.

Pop: Using the index finger (most frequently) to pluck a string with force to achieve a sound not only of the guitar naturally resonating, but with the included fret-noise and vibration that warrant the classic sound of the "pop".

X usually refers to a common "mute" sound, accomplished by covering a string lightly, and strumming or picking to achieve the sound. In this context, the X's will be slapped, popped or plucked with another finger to create a percussive distinction.

Using the notation to grasp the technique, in my opinion, will be much less effective than analyzing the demonstration video, so be sure to pay close attention to what's being done.